Intercooler piping diameter
 

I'm in the process of redoing my entire setup. Originally I had a 3 inch outlet from my turbo going to a 2.5 inch intercooler hotside, to 2.5 coldside, and back to 3 inch intercooler piping. While redoing my setup I initially wanted to do 3 inch endtanks on the intercooler to match the piping, but the new turbo outlet is 2.5 inch.

My question is, how does piping and endtank diameters affect performance/response/lag? My car will be street/backroad driven, but I'll be boosting 30+ psi max on a efr9180.

I have the same question. I was thinking a 2.5 to 3 elbow welded on the compressor outlet then 3 inch piping all the way. OR keep the hot side at 2.5 then exit on the cold side at 3 inch.

ideally you'd want at least the same diameter from the turbo to the IC and then kind of the same on the other side. for instance the Greddy throttle body elbow is 70mm (or 80mm if you cut it) so you'd want to run at least that size pipe on that side.

On the hot side I would keep piping the same diameter as the turbo discharge all the way to the IC. Personally I'd probably want to keep the cold side about the same size as well, but if/when you do need to expand the piping I'd do everything I could to keep that angle to approx 7°, iirc that is the ideal expansion rate to not disrupt flow or cause unneeded turbulence.

I just did a quick search of the internet and found some information on flow through a pipe.

From using a calculator at 30 psi, 3 inch diameter pipe, and 10' of pipe, max flow was 3,587 SCFM

At 2.5 inch diameter pipe, 30 psi, and 10' of pipe, max flow was 2,274 SCFM

I also found that 1000 SCFM = 74.92 lb/min

Since the EFR9180 has a max flow of 95/min, you would need a minimum of 1,268 SCFM through cold side piping.

So I would say either way you do it, you should have more than enough pipe volume to flow that turbo.

This is just a 2 minute search online, and i'm sure that there is much more to these calculations that when figuring in heat, expansion, etc.... Just bored :)

the 30 psi value in the flow equation is the pressure drop across the length of pipe. Optimally you want zero....
However, if you are moving air, or any fluid through a pipe there will never be zero pressure drop.
What you need to calculate is, how much pressure drop is there in a given size pipe at your maximum flow rate?
There are other factors to consider. One is volume, and it effect responsiveness. Too much volume creates lag.
Another is fitment.

If you are planning on running 30 psi i would do 3 in both, but most inport is you intercooler sizing and quality. The less pressure drop through the system, the beter. What intercooler core and size are you planing on running?

i was looking for something else and ran across this https://www.rx7club.com/2nd-generati...d-help-762492/

the author of that post goes on to calculate the flow at .42 mach. he then calculated the mass airflow at atmospheric pressure. When boosted, air density increases, the primary factors are pressure and temperature. So at 15psi boost you would have nearly double the mass airflow he calculated.

I currently have the intercooler that came with the Defined Autoworks VMIC kit (generic Godspeed core). I'm assuming I'll need to upgrade it for proper efficiency at the power/psi I want to run?

You may want a 4" or 4.5" thick cooler core depending on the space you have under the hood. I have heard good things about CFS and HKS cores.

I am assuming the 30+psig is intake manifold pressure? This is a different pressure than at the turbo outlet, the hot side of the IC, the cold side of the IC, and at the throttle body. Due to short runs of piping in cars, there are a lot of pressure drop areas that will have on effect of your turbo's max limit. This means that the pressure needed at the turbo outlet will be higher. Additionally, larger diameter piping and larger core IC will increase turbo lag as that is more volume that the turbo needs to pressurize. Larger piping may decrease pressure drop throughout the system due to lower velocities (means less friction) but again more lag. Also, a larger IC will result in a slower velocity allowing for more turbulence, longer dwell time, and higher temperature drop (assuming you are not heat soaking it) but larger pressure drop across it (maybe: lower velocities means lower fiction loss means less pressure drop; this can get into a research paper). Typically you want a 1 to 1.5 psig drop over an IC. This means a good temp drop and it is working efficiently. If you do increase pipe size, this will allow for a slight temperature drop in the air pressure, but probably negligible. With a street set up, I wouldn't put too much on flow and be more interested in turbo lag as you will be starting from low pressure without pre-spooling. If you just want to brag about what the dyno says, go with larger piping and see how much top end power you can get with single pulls. But if you are worried about lag and doing street driving (lag is not fun on the street), than keep the size smaller and upgrade to a better IC as you will need better cooling on the street. Maybe a custom with tapered ends. If you are spending the cash for a "reliable" 30+psig, spend the money on a good IC so you don't over heat things. What was your set up before the new turbo? What pressures were you running? You may be surprised about the range a IC can still be efficient at. It's just piping. You can always upgrade to 3" pipe if you think the pressure drop due to friction is too much.

Specifically...... lower velocities means lower fiction loss means less pressure drop.....

Drag increases with the square of velocity. It's the same outside a body moving through air or moving air through a pipe.
The link earlier in this thread referenced Corky Bell saying you should avoid exceeding mach.42. I think if your getting near that, let's talk bigger pipes.

This is great information. I'll have to message Defined to see what the intercooler is rated to. I can't seem to find it on their page.

I have the same intercooler and I'm hesitant to replace my M2/ASP large with it, just from looking at it the M2 looks to be a better core and has 2.75" in and out, I may just adapt it or make my own.

But, maybe we shouldn't be too quick to dismiss the Godspeed IC capabilities, there's at least one instance of this kit getting to 600 whp, how efficient? Would it be higher with a different IC? Who knows....